7 %% http://www.michaelshell.org/
8 %% for current contact information.
10 %% This is a skeleton file demonstrating the use of IEEEtran.cls
11 %% (requires IEEEtran.cls version 1.7 or later) with an IEEE conference paper.
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42 %% File list of work: IEEEtran.cls, IEEEtran_HOWTO.pdf, bare_adv.tex,
43 %% bare_conf.tex, bare_jrnl.tex, bare_jrnl_compsoc.tex
44 %%*************************************************************************
46 % *** Authors should verify (and, if needed, correct) their LaTeX system ***
47 % *** with the testflow diagnostic prior to trusting their LaTeX platform ***
48 % *** with production work. IEEE's font choices can trigger bugs that do ***
49 % *** not appear when using other class files. ***
50 % The testflow support page is at:
51 % http://www.michaelshell.org/tex/testflow/
55 % Note that the a4paper option is mainly intended so that authors in
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62 % Also note that the "draftcls" or "draftclsnofoot", not "draft", option
63 % should be used if it is desired that the figures are to be displayed in
66 \documentclass[conference,pdf,a4paper,10pt,final,twoside,twocolumn]{IEEEtran}
67 % Add the compsoc option for Computer Society conferences.
69 % If IEEEtran.cls has not been installed into the LaTeX system files,
70 % manually specify the path to it like:
71 % \documentclass[conference]{../sty/IEEEtran}
73 % Some very useful LaTeX packages include:
74 % (uncomment the ones you want to load)
76 % *** MISC UTILITY PACKAGES ***
79 % Heiko Oberdiek's ifpdf.sty is very useful if you need conditional
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87 % The latest version of ifpdf.sty can be obtained from:
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102 % cite.sty was written by Donald Arseneau
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104 % \cite{} output to follow that of IEEE. Loading the cite package will
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109 % noadjust option (cite.sty V3.8 and later) if you want to turn this off.
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130 % \DeclareGraphicsExtensions{.pdf,.jpeg,.png}
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159 % You can find documentation about the pdfTeX application at:
160 % http://www.tug.org/applications/pdftex
166 % *** MATH PACKAGES ***
168 %\usepackage[cmex10]{amsmath}
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189 % *** SPECIALIZED LIST PACKAGES ***
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204 % Also of interest may be the (relatively newer and more customizable)
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211 % *** ALIGNMENT PACKAGES ***
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231 % http://www.ctan.org/tex-archive/macros/latex/contrib/mdwtools/
234 % IEEEtran contains the IEEEeqnarray family of commands that can be used to
235 % generate multiline equations as well as matrices, tables, etc., of high
239 %\usepackage{eqparbox}
240 % Also of notable interest is Scott Pakin's eqparbox package for creating
241 % (automatically sized) equal width boxes - aka "natural width parboxes".
243 % http://www.ctan.org/tex-archive/macros/latex/contrib/eqparbox/
249 % *** SUBFIGURE PACKAGES ***
250 %\usepackage[tight,footnotesize]{subfigure}
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252 % easy to put subfigures in your figures. e.g., "Figure 1a and 1b". For IEEE
253 % work, it is a good idea to load it with the tight package option to reduce
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258 % subfigure.sty has been superceeded by subfig.sty.
262 %\usepackage[caption=false]{caption}
263 %\usepackage[font=footnotesize]{subfig}
264 % subfig.sty, also written by Steven Douglas Cochran, is the modern
265 % replacement for subfigure.sty. However, subfig.sty requires and
266 % automatically loads Axel Sommerfeldt's caption.sty which will override
267 % IEEEtran.cls handling of captions and this will result in nonIEEE style
268 % figure/table captions. To prevent this problem, be sure and preload
269 % caption.sty with its "caption=false" package option. This is will preserve
270 % IEEEtran.cls handing of captions. Version 1.3 (2005/06/28) and later
271 % (recommended due to many improvements over 1.2) of subfig.sty supports
272 % the caption=false option directly:
273 %\usepackage[caption=false,font=footnotesize]{subfig}
275 % The latest version and documentation can be obtained at:
276 % http://www.ctan.org/tex-archive/macros/latex/contrib/subfig/
277 % The latest version and documentation of caption.sty can be obtained at:
278 % http://www.ctan.org/tex-archive/macros/latex/contrib/caption/
283 % *** FLOAT PACKAGES ***
285 %\usepackage{fixltx2e}
286 % fixltx2e, the successor to the earlier fix2col.sty, was written by
287 % Frank Mittelbach and David Carlisle. This package corrects a few problems
288 % in the LaTeX2e kernel, the most notable of which is that in current
289 % LaTeX2e releases, the ordering of single and double column floats is not
290 % guaranteed to be preserved. Thus, an unpatched LaTeX2e can allow a
291 % single column figure to be placed prior to an earlier double column
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293 % http://www.ctan.org/tex-archive/macros/latex/base/
297 %\usepackage{stfloats}
298 % stfloats.sty was written by Sigitas Tolusis. This package gives LaTeX2e
299 % the ability to do double column floats at the bottom of the page as well
300 % as the top. (e.g., "\begin{figure*}[!b]" is not normally possible in
301 % LaTeX2e). It also provides a command:
303 % to enable the placement of footnotes below bottom floats (the standard
304 % LaTeX2e kernel puts them above bottom floats). This is an invasive package
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309 % Documentation is contained in the stfloats.sty comments as well as in the
310 % presfull.pdf file. Do not use the stfloats baselinefloat ability as IEEE
311 % does not allow \baselineskip to stretch. Authors submitting work to the
312 % IEEE should note that IEEE rarely uses double column equations and
313 % that authors should try to avoid such use. Do not be tempted to use the
314 % cuted.sty or midfloat.sty packages (also by Sigitas Tolusis) as IEEE does
315 % not format its papers in such ways.
321 % *** PDF, URL AND HYPERLINK PACKAGES ***
324 % url.sty was written by Donald Arseneau. It provides better support for
325 % handling and breaking URLs. url.sty is already installed on most LaTeX
326 % systems. The latest version can be obtained at:
327 % http://www.ctan.org/tex-archive/macros/latex/contrib/misc/
328 % Read the url.sty source comments for usage information. Basically,
335 % *** Do not adjust lengths that control margins, column widths, etc. ***
336 % *** Do not use packages that alter fonts (such as pslatex). ***
337 % There should be no need to do such things with IEEEtran.cls V1.6 and later.
338 % (Unless specifically asked to do so by the journal or conference you plan
339 % to submit to, of course. )
341 % correct bad hyphenation here
342 \hyphenation{op-tical net-works semi-conduc-tor}
344 % Macro for certain acronyms in small caps. Doesn't work with the
345 % default font, though (it contains no smallcaps it seems).
346 \def\acro#1{{\small{#1}}}
347 \def\VHDL{\acro{VHDL}}
349 \def\CLaSH{{\small{C}}$\lambda$a{\small{SH}}}
351 % Macro for pretty printing haskell snippets. Just monospaced for now, perhaps
352 % we'll get something more complex later on.
353 \def\hs#1{\texttt{#1}}
354 \def\quote#1{``{#1}"}
356 \newenvironment{xlist}[1][\rule{0em}{0em}]{%
358 \settowidth{\labelwidth}{#1:}
359 \setlength{\labelsep}{0.5cm}
360 \setlength{\leftmargin}{\labelwidth}
361 \addtolength{\leftmargin}{\labelsep}
362 \setlength{\rightmargin}{0pt}
363 \setlength{\parsep}{0.5ex plus 0.2ex minus 0.1ex}
364 \setlength{\itemsep}{0 ex plus 0.2ex}
365 \renewcommand{\makelabel}[1]{##1:\hfil}
370 \usepackage{paralist}
372 %include polycode.fmt
377 % can use linebreaks \\ within to get better formatting as desired
378 \title{C$\lambda$aSH: Structural Descriptions \\ of Synchronous Hardware using Haskell}
381 % author names and affiliations
382 % use a multiple column layout for up to three different
384 \author{\IEEEauthorblockN{Christiaan P.R. Baaij, Matthijs Kooijman, Jan Kuper, Marco E.T. Gerards, Bert Molenkamp, Sabih H. Gerez}
385 \IEEEauthorblockA{University of Twente, Department of EEMCS\\
386 P.O. Box 217, 7500 AE, Enschede, The Netherlands\\
387 c.p.r.baaij@@utwente.nl, matthijs@@stdin.nl}}
389 % \IEEEauthorblockN{Homer Simpson}
390 % \IEEEauthorblockA{Twentieth Century Fox\\
392 % Email: homer@thesimpsons.com}
394 % \IEEEauthorblockN{James Kirk\\ and Montgomery Scott}
395 % \IEEEauthorblockA{Starfleet Academy\\
396 % San Francisco, California 96678-2391\\
397 % Telephone: (800) 555--1212\\
398 % Fax: (888) 555--1212}}
400 % conference papers do not typically use \thanks and this command
401 % is locked out in conference mode. If really needed, such as for
402 % the acknowledgment of grants, issue a \IEEEoverridecommandlockouts
403 % after \documentclass
405 % for over three affiliations, or if they all won't fit within the width
406 % of the page, use this alternative format:
408 %\author{\IEEEauthorblockN{Michael Shell\IEEEauthorrefmark{1},
409 %Homer Simpson\IEEEauthorrefmark{2},
410 %James Kirk\IEEEauthorrefmark{3},
411 %Montgomery Scott\IEEEauthorrefmark{3} and
412 %Eldon Tyrell\IEEEauthorrefmark{4}}
413 %\IEEEauthorblockA{\IEEEauthorrefmark{1}School of Electrical and Computer Engineering\\
414 %Georgia Institute of Technology,
415 %Atlanta, Georgia 30332--0250\\ Email: see http://www.michaelshell.org/contact.html}
416 %\IEEEauthorblockA{\IEEEauthorrefmark{2}Twentieth Century Fox, Springfield, USA\\
417 %Email: homer@thesimpsons.com}
418 %\IEEEauthorblockA{\IEEEauthorrefmark{3}Starfleet Academy, San Francisco, California 96678-2391\\
419 %Telephone: (800) 555--1212, Fax: (888) 555--1212}
420 %\IEEEauthorblockA{\IEEEauthorrefmark{4}Tyrell Inc., 123 Replicant Street, Los Angeles, California 90210--4321}}
425 % use for special paper notices
426 %\IEEEspecialpapernotice{(Invited Paper)}
431 % make the title area
437 The abstract goes here.
439 % IEEEtran.cls defaults to using nonbold math in the Abstract.
440 % This preserves the distinction between vectors and scalars. However,
441 % if the conference you are submitting to favors bold math in the abstract,
442 % then you can use LaTeX's standard command \boldmath at the very start
443 % of the abstract to achieve this. Many IEEE journals/conferences frown on
444 % math in the abstract anyway.
451 % For peer review papers, you can put extra information on the cover
453 % \ifCLASSOPTIONpeerreview
454 % \begin{center} \bfseries EDICS Category: 3-BBND \end{center}
457 % For peerreview papers, this IEEEtran command inserts a page break and
458 % creates the second title. It will be ignored for other modes.
459 \IEEEpeerreviewmaketitle
462 \section{Introduction}
463 Hardware description languages has allowed the productivity of hardware
464 engineers to keep pace with the development of chip technology. Standard
465 Hardware description languages, like \VHDL\ and Verilog, allowed an engineer
466 to describe circuits using a programming language. These standard languages
467 are very good at describing detailed hardware properties such as timing
468 behavior, but are generally cumbersome in expressing higher-level
469 abstractions. These languages also tend to have a complex syntax and a lack of
470 formal semantics. To overcome these complexities, and raise the abstraction
471 level, a great number of approaches based on functional languages has been
472 proposed \cite{T-Ruby,Hydra,HML2,Hawk1,Lava,ForSyDe1,Wired,reFLect}. The idea
473 of using functional languages started in the early 1980s \cite{Cardelli1981,
474 muFP,DAISY,FHDL}, a time which also saw the birth of the currently popular
475 hardware description languages such as \VHDL.
477 What gives functional languages as hardware description languages their merits
478 is the fact that basic combinatorial circuits are equivalent to mathematical
479 function, and that functional languages lend themselves very well to describe
480 and compose these mathematical functions.
481 \section{Hardware description in Haskell}
483 \subsection{Function application}
484 The basic syntactic elements of a functional program are functions
485 and function application. These have a single obvious \VHDL\
486 translation: each top level function becomes a hardware component,
487 where each argument is an input port and the result value is the
488 (single) output port. This output port can have a complex type (such
489 as a tuple), so having just a single output port does not create a
492 Each function application in turn becomes component instantiation.
493 Here, the result of each argument expression is assigned to a
494 signal, which is mapped to the corresponding input port. The output
495 port of the function is also mapped to a signal, which is used as
496 the result of the application itself.
498 Since every top level function generates its own component, the
499 hierarchy of of function calls is reflected in the final \VHDL\
500 output as well, creating a hierarchical \VHDL\ description of the
501 hardware. This separation in different components makes the
502 resulting \VHDL\ output easier to read and debug.
504 Example that defines the \texttt{mac} function by applying the
505 \texttt{add} and \texttt{mul} functions to calculate $a * b + c$:
508 mac a b c = add (mul a b) c
513 \subsection{Choices }
514 Although describing components and connections allows describing a
515 lot of hardware designs already, there is an obvious thing missing:
516 choice. We need some way to be able to choose between values based
517 on another value. In Haskell, choice is achieved by \hs{case}
518 expressions, \hs{if} expressions, pattern matching and guards.
520 The easiest of these are of course case expressions (and \hs{if}
521 expressions, which can be very directly translated to \hs{case}
522 expressions). A \hs{case} expression can in turn simply be
523 translated to a conditional assignment in \VHDL, where the
524 conditions use equality comparisons against the constructors in the
525 \hs{case} expressions.
527 A slightly more complex (but very powerful) form of choice is
528 pattern matching. A function can be defined in multiple clauses,
529 where each clause specifies a pattern. When the arguments match the
530 pattern, the corresponding clause will be used.
532 A pattern match (with optional guards) can also be implemented using
533 conditional assignments in \VHDL, where the condition is the logical
534 and of comparison results of each part of the pattern as well as the
537 Contrived example that sums two values when they are equal or
538 non-equal (depending on the predicate given) and returns 0
539 otherwise. This shows three implementations, one using and if
540 expression, one using only case expressions and one using pattern
544 sumif pred a b = if pred == Eq && a == b || pred == Neq && a != b
550 sumif pred a b = case pred of
554 Neq -> case a != b of
560 sumif Eq a b | a == b = a + b
561 sumif Neq a b | a != b = a + b
568 Translation of two most basic functional concepts has been
569 discussed: function application and choice. Before looking further
570 into less obvious concepts like higher-order expressions and
571 polymorphism, the possible types that can be used in hardware
572 descriptions will be discussed.
574 Some way is needed to translate every values used to its hardware
575 equivalents. In particular, this means a hardware equivalent for
576 every \emph{type} used in a hardware description is needed
578 Since most functional languages have a lot of standard types that
579 are hard to translate (integers without a fixed size, lists without
580 a static length, etc.), a number of \quote{built-in} types will be
581 defined first. These types are built-in in the sense that our
582 compiler will have a fixed \VHDL\ type for these. User defined types,
583 on the other hand, will have their hardware type derived directly
584 from their Haskell declaration automatically, according to the rules
587 \subsection{Built-in types}
588 The language currently supports the following built-in types. Of these,
589 only the \hs{Bool} type is supported by Haskell out of the box (the
590 others are defined by the \CLaSH\ package, so they are user-defined types
591 from Haskell's point of view).
595 This is the most basic type available. It is mapped directly onto
596 the \texttt{std\_logic} \VHDL\ type. Mapping this to the
597 \texttt{bit} type might make more sense (since the Haskell version
598 only has two values), but using \texttt{std\_logic} is more standard
599 (and allowed for some experimentation with don't care values)
602 This is the only built-in Haskell type supported and is translated
603 exactly like the Bit type (where a value of \hs{True} corresponds to a
604 value of \hs{High}). Supporting the Bool type is particularly
605 useful to support \hs{if ... then ... else ...} expressions, which
606 always have a \hs{Bool} value for the condition.
608 A \hs{Bool} is translated to a \texttt{std\_logic}, just like \hs{Bit}.
609 \item[\hs{SizedWord}, \hs{SizedInt}]
610 These are types to represent integers. A \hs{SizedWord} is unsigned,
611 while a \hs{SizedInt} is signed. These types are parametrized by a
612 length type, so you can define an unsigned word of 32 bits wide as
616 type Word32 = SizedWord D32
619 Here, a type synonym \hs{Word32} is defined that is equal to the
620 \hs{SizedWord} type constructor applied to the type \hs{D32}. \hs{D32}
621 is the \emph{type level representation} of the decimal number 32,
622 making the \hs{Word32} type a 32-bit unsigned word.
624 These types are translated to the \VHDL\ \texttt{unsigned} and
625 \texttt{signed} respectively.
627 This is a vector type, that can contain elements of any other type and
628 has a fixed length. It has two type parameters: its
629 length and the type of the elements contained in it. By putting the
630 length parameter in the type, the length of a vector can be determined
631 at compile time, instead of only at run-time for conventional lists.
633 The \hs{Vector} type constructor takes two type arguments: the length
634 of the vector and the type of the elements contained in it. The state
635 type of an 8 element register bank would then for example be:
638 type RegisterState = Vector D8 Word32
641 Here, a type synonym \hs{RegisterState} is defined that is equal to
642 the \hs{Vector} type constructor applied to the types \hs{D8} (The type
643 level representation of the decimal number 8) and \hs{Word32} (The 32
644 bit word type as defined above). In other words, the
645 \hs{RegisterState} type is a vector of 8 32-bit words.
647 A fixed size vector is translated to a \VHDL\ array type.
648 \item[\hs{RangedWord}]
649 This is another type to describe integers, but unlike the previous
650 two it has no specific bit-width, but an upper bound. This means that
651 its range is not limited to powers of two, but can be any number.
652 A \hs{RangedWord} only has an upper bound, its lower bound is
653 implicitly zero. There is a lot of added implementation complexity
654 when adding a lower bound and having just an upper bound was enough
655 for the primary purpose of this type: type-safely indexing vectors.
657 To define an index for the 8 element vector above, we would do:
660 type RegisterIndex = RangedWord D7
663 Here, a type synonym \hs{RegisterIndex} is defined that is equal to
664 the \hs{RangedWord} type constructor applied to the type \hs{D7}. In
665 other words, this defines an unsigned word with values from
666 0 to 7 (inclusive). This word can be be used to index the
667 8 element vector \hs{RegisterState} above.
669 This type is translated to the \texttt{unsigned} \VHDL type.
671 \subsection{User-defined types}
672 There are three ways to define new types in Haskell: algebraic
673 data-types with the \hs{data} keyword, type synonyms with the \hs{type}
674 keyword and type renamings with the \hs{newtype} keyword. \GHC\
675 offers a few more advanced ways to introduce types (type families,
676 existential typing, {\small{GADT}}s, etc.) which are not standard
677 Haskell. These will be left outside the scope of this research.
679 Only an algebraic datatype declaration actually introduces a
680 completely new type, for which we provide the \VHDL\ translation
681 below. Type synonyms and renamings only define new names for
682 existing types (where synonyms are completely interchangeable and
683 renamings need explicit conversion). Therefore, these do not need
684 any particular \VHDL\ translation, a synonym or renamed type will
685 just use the same representation as the original type. The
686 distinction between a renaming and a synonym does no longer matter
687 in hardware and can be disregarded in the generated \VHDL.
689 For algebraic types, we can make the following distinction:
692 \item[\textbf{Product types}]
693 A product type is an algebraic datatype with a single constructor with
694 two or more fields, denoted in practice like (a,b), (a,b,c), etc. This
695 is essentially a way to pack a few values together in a record-like
696 structure. In fact, the built-in tuple types are just algebraic product
697 types (and are thus supported in exactly the same way).
699 The \quote{product} in its name refers to the collection of values
700 belonging to this type. The collection for a product type is the
701 Cartesian product of the collections for the types of its fields.
703 These types are translated to \VHDL\ record types, with one field for
704 every field in the constructor. This translation applies to all single
705 constructor algebraic data-types, including those with just one
706 field (which are technically not a product, but generate a VHDL
707 record for implementation simplicity).
708 \item[\textbf{Enumerated types}]
709 An enumerated type is an algebraic datatype with multiple constructors, but
710 none of them have fields. This is essentially a way to get an
711 enumeration-like type containing alternatives.
713 Note that Haskell's \hs{Bool} type is also defined as an
714 enumeration type, but we have a fixed translation for that.
716 These types are translated to \VHDL\ enumerations, with one value for
717 each constructor. This allows references to these constructors to be
718 translated to the corresponding enumeration value.
719 \item[\textbf{Sum types}]
720 A sum type is an algebraic datatype with multiple constructors, where
721 the constructors have one or more fields. Technically, a type with
722 more than one field per constructor is a sum of products type, but
723 for our purposes this distinction does not really make a
724 difference, so this distinction is note made.
726 The \quote{sum} in its name refers again to the collection of values
727 belonging to this type. The collection for a sum type is the
728 union of the the collections for each of the constructors.
730 Sum types are currently not supported by the prototype, since there is
731 no obvious \VHDL\ alternative. They can easily be emulated, however, as
732 we will see from an example:
735 data Sum = A Bit Word | B Word
738 An obvious way to translate this would be to create an enumeration to
739 distinguish the constructors and then create a big record that
740 contains all the fields of all the constructors. This is the same
741 translation that would result from the following enumeration and
742 product type (using a tuple for clarity):
746 type Sum = (SumC, Bit, Word, Word)
749 Here, the \hs{SumC} type effectively signals which of the latter three
750 fields of the \hs{Sum} type are valid (the first two if \hs{A}, the
751 last one if \hs{B}), all the other ones have no useful value.
753 An obvious problem with this naive approach is the space usage: the
754 example above generates a fairly big \VHDL\ type. Since we can be
755 sure that the two \hs{Word}s in the \hs{Sum} type will never be valid
756 at the same time, this is a waste of space.
758 Obviously, duplication detection could be used to reuse a
759 particular field for another constructor, but this would only
760 partially solve the problem. If two fields would be, for
761 example, an array of 8 bits and an 8 bit unsigned word, these are
762 different types and could not be shared. However, in the final
763 hardware, both of these types would simply be 8 bit connections,
764 so we have a 100\% size increase by not sharing these.
768 A very important concept in hardware it the concept of state. In a
769 stateful design, the outputs depend on the history of the inputs, or the
770 state. State is usually stored in registers, which retain their value
771 during a clock cycle. As we want to describe more than simple
772 combinatorial designs, \CLaSH\ needs an abstraction mechanism for state.
774 An important property in Haskell, and in most other functional languages,
775 is \emph{purity}. A function is said to be \emph{pure} if it satisfies two
778 \item given the same arguments twice, it should return the same value in
780 \item when the function is called, it should not have observable
783 This purity property is important for functional languages, since it
784 enables all kinds of mathematical reasoning that could not be guaranteed
785 correct for impure functions. Pure functions are as such a perfect match
786 for a combinatorial circuit, where the output solely depends on the
787 inputs. When a circuit has state however, it can no longer be simply
788 described by a pure function. Simply removing the purity property is not a
789 valid option, as the language would then lose many of it mathematical
790 properties. In an effort to include the concept of state in pure
791 functions, the current value of the state is made an argument of the
792 function; the updated state becomes part of the result.
794 A simple example is the description of an accumulator circuit:
796 acc :: Word -> State Word -> (State Word, Word)
797 acc inp (State s) = (State s', outp)
802 This approach makes the state of a function very explicit: which variables
803 are part of the state is completely determined by the type signature. This
804 approach to state is well suited to be used in combination with the
805 existing code and language features, such as all the choice elements, as
806 state values are just normal values.
807 \section{\CLaSH\ prototype}
811 \section{Related work}
812 Many functional hardware description languages have been developed over the
813 years. Early work includes such languages as $\mu$\acro{FP}~\cite{muFP}, an
814 extension of Backus' \acro{FP} language to synchronous streams, designed
815 particularly for describing and reasoning about regular circuits. The
816 Ruby~\cite{Ruby} language uses relations, instead of functions, to describe
817 circuits, and has a particular focus on layout. \acro{HML}~\cite{HML2} is a
818 hardware modeling language based on the strict functional language
819 \acro{ML}, and has support for polymorphic types and higher-order functions.
820 Published work suggests that there is no direct simulation support for
821 \acro{HML}, and that the translation to \VHDL\ is only partial.
823 Like this work, many functional hardware description languages have some sort
824 of foundation in the functional programming language Haskell.
825 Hawk~\cite{Hawk1} uses Haskell to describe system-level executable
826 specifications used to model the behavior of superscalar microprocessors. Hawk
827 specifications can be simulated, but there seems to be no support for
828 automated circuit synthesis. The ForSyDe~\cite{ForSyDe2} system uses Haskell
829 to specify abstract system models, which can (manually) be transformed into an
830 implementation model using semantic preserving transformations. ForSyDe has
831 several simulation and synthesis backends, though synthesis is restricted to
832 the synchronous subset of the ForSyDe language.
834 Lava~\cite{Lava} is a hardware description language that focuses on the
835 structural representation of hardware. Besides support for simulation and
836 circuit synthesis, Lava descriptions can be interfaced with formal method
837 tools for formal verification. Lava descriptions are actually circuit
838 generators when viewed from a synthesis viewpoint, in that the language
839 elements of Haskell, such as choice, can be used to guide the circuit
840 generation. If a developer wants to insert a choice element inside an actual
841 circuit he will have to specify this explicitly as a component. In this
842 respect \CLaSH\ differs from Lava, in that all the choice elements, such as
843 case-statements and patter matching, are synthesized to choice elements in the
844 eventual circuit. As such, richer control structures can both be specified and
845 synthesized in \CLaSH\ compared to any of the languages mentioned in this
848 The merits of polymorphic typing, combined with higher-order functions, are
849 now also recognized in the `main-stream' hardware description languages,
850 exemplified by the new \VHDL\ 2008 standard~\cite{VHDL2008}. \VHDL-2008 has
851 support to specify types as generics, thus allowing a developer to describe
852 polymorphic components. Note that those types still require an explicit
853 generic map, whereas type-inference and type-specialization are implicit in
856 Wired~\cite{Wired},, T-Ruby~\cite{T-Ruby}, Hydra~\cite{Hydra}.
858 A functional language designed specifically for hardware design is
859 $re{\mathit{FL}}^{ect}$~\cite{reFLect}, which draws experience from earlier
860 language called \acro{FL}~\cite{FL} to la
862 % An example of a floating figure using the graphicx package.
863 % Note that \label must occur AFTER (or within) \caption.
864 % For figures, \caption should occur after the \includegraphics.
865 % Note that IEEEtran v1.7 and later has special internal code that
866 % is designed to preserve the operation of \label within \caption
867 % even when the captionsoff option is in effect. However, because
868 % of issues like this, it may be the safest practice to put all your
869 % \label just after \caption rather than within \caption{}.
871 % Reminder: the "draftcls" or "draftclsnofoot", not "draft", class
872 % option should be used if it is desired that the figures are to be
873 % displayed while in draft mode.
877 %\includegraphics[width=2.5in]{myfigure}
878 % where an .eps filename suffix will be assumed under latex,
879 % and a .pdf suffix will be assumed for pdflatex; or what has been declared
880 % via \DeclareGraphicsExtensions.
881 %\caption{Simulation Results}
885 % Note that IEEE typically puts floats only at the top, even when this
886 % results in a large percentage of a column being occupied by floats.
889 % An example of a double column floating figure using two subfigures.
890 % (The subfig.sty package must be loaded for this to work.)
891 % The subfigure \label commands are set within each subfloat command, the
892 % \label for the overall figure must come after \caption.
893 % \hfil must be used as a separator to get equal spacing.
894 % The subfigure.sty package works much the same way, except \subfigure is
895 % used instead of \subfloat.
898 %\centerline{\subfloat[Case I]\includegraphics[width=2.5in]{subfigcase1}%
899 %\label{fig_first_case}}
901 %\subfloat[Case II]{\includegraphics[width=2.5in]{subfigcase2}%
902 %\label{fig_second_case}}}
903 %\caption{Simulation results}
907 % Note that often IEEE papers with subfigures do not employ subfigure
908 % captions (using the optional argument to \subfloat), but instead will
909 % reference/describe all of them (a), (b), etc., within the main caption.
912 % An example of a floating table. Note that, for IEEE style tables, the
913 % \caption command should come BEFORE the table. Table text will default to
914 % \footnotesize as IEEE normally uses this smaller font for tables.
915 % The \label must come after \caption as always.
918 %% increase table row spacing, adjust to taste
919 %\renewcommand{\arraystretch}{1.3}
920 % if using array.sty, it might be a good idea to tweak the value of
921 % \extrarowheight as needed to properly center the text within the cells
922 %\caption{An Example of a Table}
923 %\label{table_example}
925 %% Some packages, such as MDW tools, offer better commands for making tables
926 %% than the plain LaTeX2e tabular which is used here.
927 %\begin{tabular}{|c||c|}
937 % Note that IEEE does not put floats in the very first column - or typically
938 % anywhere on the first page for that matter. Also, in-text middle ("here")
939 % positioning is not used. Most IEEE journals/conferences use top floats
940 % exclusively. Note that, LaTeX2e, unlike IEEE journals/conferences, places
941 % footnotes above bottom floats. This can be corrected via the \fnbelowfloat
942 % command of the stfloats package.
947 The conclusion goes here.
952 % conference papers do not normally have an appendix
955 % use section* for acknowledgement
956 \section*{Acknowledgment}
959 The authors would like to thank...
965 % trigger a \newpage just before the given reference
966 % number - used to balance the columns on the last page
967 % adjust value as needed - may need to be readjusted if
968 % the document is modified later
969 %\IEEEtriggeratref{8}
970 % The "triggered" command can be changed if desired:
971 %\IEEEtriggercmd{\enlargethispage{-5in}}
975 % can use a bibliography generated by BibTeX as a .bbl file
976 % BibTeX documentation can be easily obtained at:
977 % http://www.ctan.org/tex-archive/biblio/bibtex/contrib/doc/
978 % The IEEEtran BibTeX style support page is at:
979 % http://www.michaelshell.org/tex/ieeetran/bibtex/
980 \bibliographystyle{IEEEtran}
981 % argument is your BibTeX string definitions and bibliography database(s)
982 \bibliography{IEEEabrv,clash.bib}
984 % <OR> manually copy in the resultant .bbl file
985 % set second argument of \begin to the number of references
986 % (used to reserve space for the reference number labels box)
987 % \begin{thebibliography}{1}
989 % \bibitem{IEEEhowto:kopka}
990 % H.~Kopka and P.~W. Daly, \emph{A Guide to \LaTeX}, 3rd~ed.\hskip 1em plus
991 % 0.5em minus 0.4em\relax Harlow, England: Addison-Wesley, 1999.
993 % \end{thebibliography}
1001 % vim: set ai sw=2 sts=2 expandtab: